In the past, a magnetic recording medium which is prepared by dispersing ferromagnetic metal oxide particles of acicular crystals such as .gamma.-Fe.sub.2 O.sub.3, Co-containing magnetic iron oxide or CrO.sub.2 in a binder, and coating the thus obtained dispersion on a non-magnetic support to provide a magnetic layer has generally been used as a magnetic recording medium for audio recording, video recording and for computers (hereinafter referred to as a magnetic tape in some cases). However, with recent increased demand for high density recording on the magnetic recording medium, ferromagnetic alloy particles have been commonly used instead of the conventionally used ferromagnetic metal oxide particles.
Ferromagnetic alloy particles are very suitable as ferromagnetic particles for a magnetic recording medium which is used not only for measuring instruments and computers, but also for audio and video tapes which require high density recording, because ferromagnetic alloy particles have high coercive force (Hc) and high residual magnetic flux density (Br) and is stable against temperature changes. It is expected, therefore, that if ferromagnetic alloy particles are made finer and finer, much higher recording density can be realized.
However, due to the low hardness of ferromagnetic alloy particles there are such problems that running durability of a magnetic layer prepared using those ferromagnetic alloy particles is insufficient in that the surface of a magnetic layer is easily scratched and ferromagnetic alloy particles on a magnetic layer are easily desorbed, thereby increasing dropouts. Thus, ferromagnetic alloy particles which are desorbed from a magnetic layer cause bridging of the magnetic head gap. Further, because of poor running durability of a magnetic layer, a still life of the magnetic layer also decreases upon a still mode where still images are continuously reproduced.
In order to improve running durability of a magnetic layer of a magnetic recording medium using ferromagnetic alloy particles, while keeping good electromagnetic properties thereof, it has been proposed in U.S. Pat. No. 3,833,412 to add abrasive agents (hard particles) such as corundum, silicon carbide or chromium oxide into the magnetic layer. In such a case, a relatively large amount of abrasive agent needs to be added to effectively improve running durability. However, the above method is not desirable because a magnetic layer containing a large amount of abrasive agents causes heavy wear out of a magnetic head and affects electromagnetic properties. Further, conventionally used abrasive agents incorporated into a magnetic layer tend to desorb, thereby causing bridging of the magnetic head gap.
That is, a satisfactory method which improves not only electromagnetic properties but also running durability without affecting characteristics of the magnetic recording medium as well as magnetic heads has not yet been obtained until now.
In thie connection, the inventors of the present invention have made extensive studies as to physical properties of abrasive agents, particularly the combination of particle size of abrasive agents and ferromagnetic alloy particles, and as a result thereof, it was found that the above-described defects can be overcome by use of finely divided inorganic particles (particle size: 0.2 .mu.m or less) which have not commonly been used and ferromagnetic alloy particles having a specific surface area of 48 m.sup.2 /g or more in combination in a specific mixing ratio.